1. Field of the Invention
The present invention relates generally to a mobile communication terminal, and in particular, to a transmission apparatus and method for reducing current consumption.
2. Description of the Related Art
In a mobile communication terminal (hereinafter, referred to as a xe2x80x9cmobile terminalxe2x80x9d for short), an RF (Radio Frequency) module is divided into a receiver and a transmitter. The receiver converts a signal received from a base station into a baseband signal and provides the baseband signal to a modem. The transmitter converts a baseband signal from the modem into an RF signal and transmits the RF signal to the base station.
For power control, the transmitter of the mobile terminal controls a gain of a signal output from a baseband analog (BBA) processor using an automatic gain control (AGC) amplifier. For example, an AGC amplifier made by Qualcomm has an operating range of about 85 dB from xe2x88x9245 dB to +40 dB. Since the maximum output power of the AGC amplifier is xe2x88x9214 dB for a gain of about 30 dB (as set forth on the data sheet for a Qualcomm-made AGC amplifier), it can be expected that the output power of the amplifier is about 6 dBm. Further, since output power of the BBA processor is xe2x88x9217 dBm, it is possible to use power of about up to 0 dBm for the output power of the amplifier. However, since there exist gains of a drive amplifier and a power amplifier on an actual transmission line budget, an attenuator (with an attenuation of 25 to 30 dB) is used at an output end of the AGC amplifier to amplify again the signal before transmission, in order to obtain a sufficient operating range. This method is disadvantageous in that the power obtained by using a battery is attenuated and then the attenuated signal is amplified again by using the battery, so that the batter is doubly wasted, causing a reduction in an operating time of the mobile terminal. Here, the dBm stands for the value of absolute power which is generated using log function at the basis of 1 mW.
FIG. 1 shows a transmission apparatus for a conventional mobile terminal, having the above-stated structure.
Referring to FIG. 1, a BBA processor 101 converts a digital signal output from a modem (not shown) into a baseband analog signal. An AGC amplifier 102 controls a gain of a signal output from the BBA processor 101 according to a control voltage provided from the modem. An attenuator 103 attenuates the output signal of the AGC amplifier 102. A mixer 104 mixes a signal output from the attenuator 103 with a frequency generated by a local oscillator (not shown) to convert the input signal into an RF signal. A filter 105 bandpass-filters the output signal of the mixer 104. A drive amplifier 106 amplifies the output signal of the filter 105. A filter 107 bandpass-filters the output signal of the drive amplifier 106. A power amplifier 108 amplifies the output signal of the filter 107 to a transmission power level. A duplexer 109 separates transmission signals from reception signals. That is, the duplexer 109 transmits the output signal of the power amplifier 108 through an antenna ANT and provides a received signal to a receiver (not shown).
The conventional mobile terminal having the above-stated structure controls transmission power in two methods. One is an open loop power control method for the controlling transmission power such that the sum of reception power Rx and transmission power Tx should pursue predetermined level of x dBm. Another is a closed-loop power control method in which the mobile terminal receives power control bits from the base station and controls the transmission power according to the received power control bits.
In the foregoing two power control methods, the modem can control the transmission power by detecting field strength of a signal received from the base station and then applying the detected field strength to the AGC amplifier 102. That is, the AGC amplifier 102 amplifies or attenuates the input signal according to the control voltage to vary the transmission power at the antenna ANT. Here, a variable range of the transmission power at the antenna ANT is referred to as a xe2x80x9cdynamic rangexe2x80x9d, and this dynamic range is determined depending on a dynamic range of the AGC amplifier 102.
However, since the transmitter of the conventional mobile terminal attenuates the signal using the attenuator 103 at an output end of the AGC amplifier 102 and then amplifies the attenuated signal contrarily at the following stages of the drive amplifier 106 and the power amplifier 108, an efficiency of the battery is inevitably decreased. In addition, the transmitter has an inefficient structure that the efficiency of the AGC amplifier 102 cannot be sufficiently utilized and instead, gains of the drive amplifier and the power amplifier are used, because of excessive attenuation by the AGC amplifier 102.
It is, therefore, an object of the present invention to provide an apparatus and method for transmitting an output signal of an AGC amplifier directly through an antenna without using a drive amplifier and a power amplifier, when output power of a mobile terminal is lower than the maximum output power of the AGC amplifier in a transmitter.
To achieve the above and other objects, there is provided a transmission apparatus for a mobile terminal. The transmission apparatus includes an automatic gain control (AGC) amplifier for AGC-amplifying an input baseband signal; an attenuator for attenuating an output signal of the AGC amplifier; a multiplier for multiplying an output signal of the attenuator by a carrier frequency signal to convert the signal into a radio frequency (RF) signal; a first filter for filtering an output signal of the multiplier; a drive amplifier for amplifying an output signal of the first filter; a second filter for filtering an output signal of the drive amplifier; a power amplifier for amplifying an output signal of the second filter; and an antenna. When output power of the mobile terminal is lower than predetermined maximum output power of the AGC amplifier, the output signal of the AGC amplifier is transmitted through the multiplier, the first filter and the antenna.
Preferably, the output power of the mobile terminal is determined depending on field strength of a signal received from a base station.
Preferably, the output power of the mobile terminal is determined depending on power control bits received from a base station.
Preferably, when the output power of the mobile terminal is lower than the predetermined maximum output power of the AGC amplifier, a power supply voltage provided to the drive amplifier and the power amplifier is blocked.